In summary, Level-5 is collaborating with Capcom on "Layton Kyouju vs Gyakuten Saiban", a game for 3DS. It seems to incorporate elements from both series; also, there's no release date yet, but there is an official site (not much on it right now, though).

Have never played a Layton game (strangely enough, at least not yet), but I love Level-5, and Ace Attorney of course, so I'll definitely be keeping an eye on this crossover.

There was a post on Capcom Unity (official Capcom site) that essentially said that the game has only been announced for Japan at this point. That might be the source of the rumor.

Personally, I'm not worried. Capcom knows that there's a devoted AA fanbase overseas, and Layton games do well outside of Japan, too. Capcom (and Level-5) would be crazy not to localize this crossover. The only potential problem might be that in the US at least, the Layton games are published by Nintendo. I'm sure they can figure something out, though.